A library apparatus is an apparatus which automatically carries out the operation of mounting a medium such as a cartridge type magnetic tape and optical disk, and is used as a mass storage for saving a large amount of files in the magnetic disk units or the like. Hence, the library apparatus is important when improving the reliability, maintainability and availability of the system. The library apparatus is made up of an access part for transporting the medium, a driver part for recording/reproducing information with respect to the medium, and a cell part for storing a plurality of mediums.
A description will be given of the operation of a conventional library apparatus in conjunction with FIG. 1. As shown in FIG. 1A, addresses 0A-3C and 4A-6D are assigned to the cells, and the drive is fixedly provided at the position of the address 3D. The access part (not shown) transports the medium which is stored in the cell having the address which is specified at the start of the job (JOB), and returns the medium back to the cell having the original address at the end of the job. FIG. 1B shows the case where the specified address is 0A.
FIG. 1C shows a move command (MOVE) which is issued with respect to the library apparatus from a central processing unit (CPU) of a host in the above described case. In this case, the move command indicates that the source address is 0A and the destination address is 3D. When the drive ends the information recording/reproduction with respect to the medium, the CPU of the host issues a move command MOVE 3D, 0A to return the medium back to the cell having the source address 0A.
Generally, the medium transport time can be considered as one factor determining the performance of the library apparatus, and this medium transport time indicates the moving time of the medium from the cell to the drive. Conventionally, the moving of the medium which is stored in the cell distant from the drive takes more time compared to the moving of the medium which is stored in the cell in the vicinity of the drive. Hence, if the job which uses the medium stored in the cell which is distant from the drive is frequently started, there was a problem in that the processing efficiency of the library apparatus may deteriorate.